Blasting Practice in the East Bluff Section of the Britannia Mine

Introduction The Britannia mine is at Britannia Beach, on Howe sound, approximately thirty miles from Vancouver. The first claims were staked in 1898, and a local company was formed at that time to develop them. In 1904, Mr. Grant B. Schley became actively interested in the property and in the following year the Britannia Mining and Smelting Company, Limited, was incorporated to operate it. This Company was taken over a few years later by the Howe Sound Company, Limited. The mine comprises five more or less separate ore-bodies, which have produced approximately 20,000,000 tons of ore to date. The East Bluff ore-body, with which the present paper deals, is well suited to large-scale mining by means of carefully placed powder blasts. It covers approximately an acre and lies in the slate footwall, in a bay produced by a fault. The hanging-wall side, on the west, forms the face of the Bluff glory-hole, which extends to the 1,200 level. A portion of this ore was available for breaking into this old glory-hole, below which four bulldoze chambers could quickly be built. Mining of this block is complicated by a very soft footwall, which 'runs' badly when broken. In stoping, care is taken to guard against the hazard of dilution by deliberately leaving a small portion of ore on the footwall. Some of this will undoubtedly be lost, but it is hoped to recover a fair amount of it after the major drawing is completed. The deposit occurs in a greenstone which has been highly silicified following brecciation. The chief minerals are chalcopyrite, sphalerite, and pyrite. Concentrates of copper, zinc, and pyrite are made at the mill. The average grade of ore runs 0.7 per cent copper, 1.5 per cent zinc, and 0.03 oz. gold per ton. The rock, which is practically a chert, is extremely hard, but shatters well. Both in stoping and drifting, holes must be closely spaced and powder used generously. Development When development work started in the East Bluff, there were no raises and only one drift on each level in this section of the mine. After blocking out the ore by thorough diamond drilling, a production of two thousand tons per day was set as a goal. To obtain this tonnage from so small an area required a great deal of carefully planned and well timed development work.